The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

VW yet to address Australian class action

Volkswagen in Germany is being asked to cooperate with courts in Australia so a class action over an emissions scam can proceed, a Sydney court has heard.

Despite publicly admitting to installing dodgy devices on millions of cars, German auto giant Volkswagen, whose subsidiary includes Audi, still hasn't advised its local operators what it will admit to following an emissions scam that engulfed the companies globally, the Federal Court heard on Thursday.

An estimated 91,000 Australian car owners were among those whose vehicles were fitted with rigging devices designed to mask the level of emissions.

Two class actions were subsequently launched against Volkswagen, Audi and Skoda on behalf of those affected.

At a Federal Court directions hearing on Thursday, the court heard that despite admitting to the scandal publicly, Volkswagen Australia's parent company in Germany was yet to advise local operators on the issue.

Justice Lindsay Foster urged the auto giant to deal with the matter as soon as possible.

"The court expects the Germans to deal with this case in Australia ... expeditiously," he said.

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The delay in legal proceedings was disappointing, lawyers acting on behalf of the Australian car owners said.

"It sits largely at odds with their (VW Australia's) apology and the public PR position of contrition and doing everything they can to do the right thing by the customers," class actions principal at Maurice Blackburn Lawyers, Jason Geisker said outside court.

"If they want to do the right thing by their customers they should immediately appear in this class action to resolve the issues".